Cathodic arc evaporation has during the last two decades come into wide commercial use for deposition of metal, alloy, and metal compound coatings. Cathodic arc discharges can also be used as plasma sources for ion processing operations such as implantation, sputter etching, reactive etching, and diffusion. A cathode of the material to be deposited is vaporized by a high current, low voltage arc plasma discharge in a vacuum chamber which has been evacuated to a pressure of typically less than 0.001 mbar. Typical arc currents range between 25 and 1000 amperes, with voltages between 15 and 50 volts. An undesirable side effect of cathodic arc evaporation is the generation of molten droplets of cathode material. These droplets are commonly called macroparticles, and range in diameter from sub-micron to tens of microns. The macroparticles can become embedded in the coating when they land on the substrate or can stick and later fall off, causing surface defects in either case.
Strategies for reducing the number of macroparticles reaching the substrate fall generally into two categories. The first is those using some form of magnetic field to control and accelerate the arc, in order to reduce macroparticle generation. The second category is those using a filtering apparatus between the cathode and the substrates which transmits at least part of the ionized vapor but blocks at least some of the molten droplets. The magnetic methods are generally simpler but do not completely eliminate macroparticle generation. The filtering methods are generally more effective at removing macroparticles, but require complex apparatus and reduce the source output significantly.
Rectangular plasma sources are desirable for the coating or ion processing of large substrates, sheet material in roll form, and for quantities of smaller substrates on a linear conveyor or circular carousel. Bi-directional sources are desirable since they increase the area over which the emitted plasma is distributed and can provide additional substrate capacity.
A publication by Aksenov, et al. ("Transport of plasma streams in a curvilinear plasma-optics system", Soviet Journal of Plasma Physics, 4(4), 1978) describes the use of a cylindrical plasma duct having a 90 degree bend, with electromagnet coils to create a solenoidal magnetic field through the duct. U.S. Pat. Nos. 5,279,723 (Falabella et al., 1994) and U.S. Pat. No. 5,433,836 (Martin, 1995) describe similar devices with cylindrical ducts with having 45 and 90 degree bends respectively. U.S. Pat. No. 4,492,845 (Kljuchko, 1985) describes a coaxial filtered arc evaporation apparatus having an annular cathode, with substrates to be coated disposed within the radius of the annular cathode. U.S. Pat. No. 4,452,686 (Axenov et al., 1984) and U.S. Pat. No. 5,282,944 (Sanders, et al., 1994) describe straight cylindrical filtering ducts with no bend, and with circular cathodes located at one end of the duct. U.S. Pat. No. 5,435,900 (Ghorokhovsky, 1995) and U.S. Pat. No. 5,840,163 (Welty, 1999) both describe filtered sources having a rectangular duct with a 90 degree bend with a cathode at one end. Sputtering cathodes having the shape of a bar of substantially rectangular cross-section, having erosion surfaces wrapping around a lengthwise periphery of the bar and having substantially bi-directional deposition distributions are disclosed in U.S. Pat. No. 4,194,962 (Chambers et al., 1980), 4,486,289 (Parsons et al., 1984) and U.S. Pat. No. 4,812,217 (George et al., 1989). Means for containing an arc on an evaporable surface are described in U.S. Pat. No. 3,793,179 (Sablev, 1974), U.S. Pat. No. 4,430,184 (Mularie, 1984), U.S. Pat. No. 5,387,326 (Buhl, 1995).